What is DDL (Data Definition Language)?
A data base schema which is specified by a set of definitions expressed by a special language is called DDL. Data Definition Language (DDL) is used to define and manage all the objects in an SQL database. 13. What is DML? Answer: It is a special language used to manipulate the Data. Data Manipulation Language (DML), which is used to select, insert, update, and delete data in the objects defined using DDL. 14. What is a PRIMARY KEY? Answer: The PRIMARY KEY is the column(s) used to uniquely identify each row of a table. 15. What is a FOREIGN KEY? Answer: A FOREIGN KEY is one or more columns whose values are based on the PRIMARY or CANDITATE KEY values from the database. 16. What is a UNIQUE KEY? Answer: A UNIQUE KEY is one or more columns that must be unique for each row of the table. 17. What is the difference between UNIQUE and PRIMARY KEY? Answer: The UNIQUE KEY column restricts entry of duplicate values but entry of NULL value is allowed. In case of PRIMARY KEY columns entry of dupli
